feat: add FillID method for Service, Route and Consumer

[czeslavo]

Adds FillID methods for Service, Route, and Consumer entities to allow setting deterministic IDs for entities based on their unique properties.

For now, it is only implemented for Service, Route and Consumer as that's what's needed on Kubernetes Ingress Controller side to generate stable IDs for analytics in Konnect.

Part of Kong/kubernetes-ingress-controller#3906.

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[codecov-commenter]

Codecov Report

Patch coverage: 60.00% and project coverage change: +0.09 🎉

Comparison is base (be56889) 52.73% compared to head (85f81c5) 52.82%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #299      +/-   ##
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+ Coverage   52.73%   52.82%   +0.09%     
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  Files          68       69       +1     
  Lines        5012     5077      +65     
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+ Hits         2643     2682      +39     
- Misses       1798     1817      +19     
- Partials      571      578       +7     

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Impacted Files	Coverage Δ
kong/ids.go	60.00% <60.00%> (ø)

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[czeslavo]

Looks like the integration tests are blocked by TestFillPluginDefaults failing consistently (not related to the code this PR introduces), #316 should fix it. Apart from that, it's ready for review.

[czeslavo]

@mmorel-35 I hope I addressed all your suggestions, PTAL.

[mmorel-35]

Would you also need to do it for plugins ?
In that case it the buildIDFor() could take as parameter the concatenation of the plugin name with the the ID of the referenced entity (Consumer, Route or Service) or just the name of the plugin when it's a global one.
I would personally add a character separator between the referenced ID and the plugin name but it might not be absolutely necessary

[czeslavo]

Would you also need to do it for plugins ? In that case it the buildIDFor() could take as parameter the concatenation of the plugin name with the the ID of the referenced entity (Consumer, Route or Service) or just the name of the plugin when it's a global one. I would personally add a character separator between the referenced ID and the plugin name but it might not be absolutely necessary

I'd rather leave it until it's going to be needed. As I mentioned in the description, we only need this function to work for Service, Route, and Consumer.